OSPF Packets and Neighbor Discovery

Hello sim!

Concerning your question “Why R1 again sending an hello packet to multicast 224.0.0.5 (sequence no 3 )”

I assume you’re talking about the cloudshark capture that Rene posted on this thread on November 8 2015. Just for reference, the cloudshark output can be found here: https://www.cloudshark.org/captures/111cb2076caa

If you’ll notice, R1 has an IP address of 192.168.12.1. Sequence number 1 shows that R1 sent a hello packet, and sequence number 3 shows another hello packet from R1. Notice the time difference of 9.8 seconds. Remember that the default hello interval for OSPF is 10 seconds. So every 10 seconds, routers are expected to send out hellos. This is normal behaviour.

And about your question “and why there is LSUPDATE packet before LSREQUEST packet ( sequence no 4 in the shark file )”

Although it is true that an LSU is sent as a response to an LSR, it can also be sent under other circumstances. So an LSU is not always the response to an LSR. So the LSU that you see at sequence number 4 is not a response to the LSR that you see at sequence number 13. The LSUs that you see at sequence numbers 14 15 and 16 are the responses to the LSR.

I hope this has been helpful!

Laz

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